The present invention relates to a liquid-filled insole for footwear.
The invention also concerns a method for making an insole for footwear, the sole at least comprising a support for the foot in the footwear, and which sole in addition comprises a net of threads disposed on top of the support, the net creating a distance between the support and the foot in the footwear, and where net is joined with the support along an outer edge of the net.
DE 296 03 914 describes an insole of this type. The insole comprises a support at the heel of the foot in the footwear. The support consists of an elastic material that may be compressed for relieving the heel. The support may be made of a foam synthetic or of cork. On top of the centre area of the support a net is disposed. The net consists of two layer of synthetic threads which are woven or knitted. The net is fastened to the support at the heel by welding. The net extends from the heel of the foot and forward right up to the toes of the foot in the footwear. From the heel and further under the metatarsus, under the ball of the foot and under the toes there is no support under the net. The net gives the possibility of air passing transversely of the net between the foot and the support of the insole and the inner sole in the footwear, respectively.
This sole implies the possibility of relieving the heel and of supplying air to the foot in the footwear. The insole has, however, some drawbacks. The net is fixed in relation to the support and in relation to the insole of the footwear. This means that air flow in the net depends on differences in moisture of the air contained in the net. This causes the air flow in the net to be very limited, implying that the parts of the foot developing the largest amount of moisture are only negligibly supplied new air. Furthermore, the net does not extend over all of the width of the sole at the heel and the metatarsus of the foot in the footwear. This implies that no exchange of air can take place laterally of the net. The comfort of the foot in the footwear is therefore very limited even though the foot rests on a net establishing a distance between the foot and the support and the inner sole of the footwear, respectively.
In U.S. Pat. No. 5,067,255, a liquid-filled insole is disclosed for cushioning and impact absorption. The insole may be covered by, for example, a fabric or leather.
Liquid-filled soles are intended to reduce and to vary the load on the foot when walking and standing. Especially by standing work, the increased movement of the foot caused by liquid-filled soles gives rise to increased excretion of foot perspiration. This causes more people to refrain from using liquid-filled soles in spite of the ergonomic advantages by using the soles.
It is the purpose of the present invention to provide a liquid-filled sole where the inconvenience by using liquid-filled soles is greatly reduced.
This purpose is achieved with an insole which is peculiar in that the support is a liquid-filled sole with a top sheet and a back sheet between which is formed a chamber containing liquid, that the outer edge of the net is joined with the top sheet and the back sheet, and that the net at least extends from an area at the heel of the foot to an area at the ball of the foot in the foot wear and at least extends over the whole width of the sole.
The method according to the invention is peculiar in that a top sheet and a back sheet are welded together at the outer edges in that a chamber containing liquid is established between the two sheets, and that the net in a subsequent step is welded together at the edge area in a position superposing the top sheet.
By providing a net on the liquid-filled sole, the increased foot perspiration arising from the use of liquid-filled sole may more easily be conducted away from the underside of the foot.
By laying the net upon a sole containing liquid between a top sheet and a back sheet, the possibility of moving the net relative to the movements of the foot is established This implies that as soon as the foot is moved, the net will also be moved, and this creates an air flow, not only transversely of the net, but also longitudinally of the net. This means that air with high humidity contained in the net, e.g. typically under the heel or under the ball of the foot, will be passed to other parts of the net, e.g. under the metatarsus or under the toes where the air humidity is not so high. This causes the air humidity to be lesser locally as the moisture is distributed over all of the longitudinal and preferably also trasversal extension of the net.
Due to the fact that net provided on liquid soles improves the ability of the net to create ventilation between the foot ent the underlying sole, the net improves the function of the liquid filled sole.
By making the insole in two steps as defined by the method according to the invention, it is possible to achieve a plane net upper side simultaneously with increasing the height in the chamber. Hereby the relief and the liquid support of the foot will be considerably increased.
Preferably, the net will extend over all the transverse extension of the sole. Hereby the outermost part of the net along the edge area will be situated outside the limits of the foot. The part of the net located outside the foot thus has a free upper side enabling discharge of air with great humidity from the interspace under the foot simultaneously with fresh air with low humidity from other parts of the footwear may be conducted into the interspaces in the net under the foot. The free edge area is thus advantageous in enabling an increased ventilation and air flow in the net of the sole.
In a preferred embodiment, the insole is peculiar in that the net comprises a coarse net and a fine net, that the coarse net consists of threads with a given greater thickness T, that the fine net consists of threads with a given lesser thickness t less than the thickness T, and that the coarse net is disposed between the top sheet and the fine net, and that the fine net is disposed on top of the coarse net.
Depending on the weaving, a coarsely woven net with thick threads is capable of containing more air and thereby more humid air than a fine net. However, the coarsely woven net also has a more rough surface. This may give rise to greater discomfort for the foot in the footwear, and may also imply more wear on stockings or socks on the foot. A finely woven net cannot contain so much air but in the opposite is more comfortable to tread on, and the risk of socks being broken is less. By laying a coarsely woven net lowermost adjacent to the top sheet and a more finely woven net facing the foot on top of the coarse net, the advantages of the coarse net will be combined with the advantages of the finer net without reducing the possibility of air to be conducted longitudinally of the sole.
In a further preferred embodiment, the insole is peculiar in that a moisture absorbing fabric coating is provided between the top sheet and the net.
By providing the top sheet with a moisture absorbing fabric coating, the airborne moisture arising in the net from the foot in the footwear will be absorbed by the fabric coating. This means that the moisture is conducted away from the foot, down through the net where the moisture is distributed longitudinally of the net each time the foot is moved, and further down to the fabric coating on the top sheet. The moisture will thus always be conducted away from the foot. When the net, when provided on a liquid sole, is capable of distributing the humid air over all of the longitudinal extension of the net, then the fabric coating will also absorb the moisture over all of the length of the fabric coating, said length at least being the same as for the net.